Cranks but won't start. Unplug ground at field spade on Alternator and it starts?

Frogurt-NM said
You stated this:

"This was the voltage regulator that had been on there for 20 years that died 3 weeks back and was replaced by the mechanical one from Napa:

https://shop.advanceautoparts.com/p...gulator-raa1052/12450617-P?selectedStore=2623

The local parts store says they can have one this afternoon."

As I'm reading through this long thread of troubleshooting, it appears to me that it all your problems started after putting in the new voltage regulator.
I would try putting in the NEW voltage regulator that matches the one that went Bad.

The no start issue comes back if battery voltage drops from car sitting over night with voltage at 12.6 volts. Battery is new. If I charge battery get it to 13 volts or more car will start.

I had parts store order another one like I had but what cane in box was old style regulator. Put that on no difference. I do have a new Standard VR128 that just came too.

There is no sense in throwing parts at it if I am seeing a 1 volt drop in Ign2 circuit and a 1.5 volt drop from alternator output to battery engine running. The cars wiring bad connection issues needs to be tracked down and fixed.

Two evenings ago I went to start car. Sounded like no spark issue then it sparked in Start position. Saw Amp Meter swing all the over to Charge shake around a bit then quickly move toward center. Battery was 14 volts before starting car. Drove car for 50 minutes AC and radio on. Amp Meter very slight lean to charge, needle still in the white gauge center, and stable at idle and cruising. Came home, shut car off, and car fired right back up. Came back out next morning battery 12.8 volts or so strong crank no start.